1. Field of the Invention
The present invention relates to a disk drive device for rotating a disk-shaped recording medium such as floppy disks.
2. Description of the Prior Art
FIG. 1 is a sectional view illustrating a spindle motor portion which is one of the major component parts of a conventional floppy disk drive (to be referred as "FDD" in this specification hereinafter). Reference numeral 1 respesents a chassis or a main body base made by the aluminum die casting process or the press; 2, a disk the surface of which the data is written and read out, and 23, 23', bearings for supporting a spindle 25 which supports and rotates the disk 2.
The disk 2 is cramped on the spindle 25 by a center cone 40. 41 indicates a bearing; 42, a center shaft which is securely carried by a pressure plate 43 by a retaining ring 44. 45 is a spring for transmitting the clamping force from the pressure plate 43 to the center cone through the bearing 41. 26 is a rotor or which driving magnets 7 are securely attached.
8 is a printed circuit board for a motor for rotating a disk. 29 are driving coils arranged in the circumferential direction and in equidistantly spaced apart and coplanar copartner relationship with each other, and the rotating force produced by using the electromagnetic conversion force produced by a conventional current switching method is imparted to the driving magnetic. 10 is a stator yoke and establishes the closed magnetic circuit together with the driving magnets 7. 11 is a magnetic head for writing and reading the data on and off from the surface of the disk 2 which is securely connected to a head carriage (not shown) so that the magnetic head can move in the directions indicated by the double pointed arrow F.
22 is a setscrew for securely attaching the rotor 26 to the spindle 25. 13 is a housing for securely holding the bearings 23 and 23' which is securely mounted on the chassis 1.
The conventional FDD of the type described above has the following problems.
(1) In the bearing assembly, the spindle 25, the bearings 23 and 23' and the rotor 26 are superposed so that the reduction in thickness of the bearing assembly is limited.
(2) The thickness of the magnetic head 11 is added to that of the motor so that the reduction in overall thickness is also limited.